1. Field of the Invention
The invention relates to a solid-state imaging device, a method of manufacturing the solid-state imaging device, and an electronic apparatus.
2. Description of the Related Art
An electronic apparatus such as a digital camera includes a solid-state imaging device. For example, the solid-state imaging device includes a CMOS (Complementary Metal Oxide Semiconductor) type image sensor and a CCD (Charge Coupled Device) type image sensor.
In the solid-state imaging device, an imaging area where a plurality of unit pixels are arrayed in a matrix shape is disposed in a semiconductor substrate. In each of the unit pixels, a photoelectric conversion portion is disposed. The photoelectric conversion portion is, for example, a photodiode and generates signal charges by receiving incident light incident through an externally attached optical system by a light-receiving plane and photoelectrically converting the light.
Among the solid-state imaging devices, in the CMOS type image sensor, the unit pixel is configured so that a plurality of transistors are included in addition to the photoelectric conversion portion. The plurality of the transistors are configured to read out the signal charges generated in the photoelectric conversion portion and to output an electrical signal to a signal line. For example, four transistors, that is, a transfer transistor, a reset transistor, an amplification transistor, and a selection transistor are disposed as the pixel transistors on the front surface of the semiconductor substrate. In addition, wire lines of electrically connecting these transistors are provided in the front surface of the semiconductor substrate.
There is a demand for solid-state imaging device may be desired to have high sensitivity. Particularly, in a digital camera used under lower luminance such as an endoscope camera and a monitoring camera, high sensitivity is necessary.
Therefore, it is considered that the high sensitivity is necessarily implemented by expanding an area of the light-receiving plane by increasing a pixel size.
In addition, there have been proposed technologies in which one set of pixel transistors is shared by a plurality of photoelectric conversion portions, so that high sensitivity is implemented by increasing an area occupied by the light-receiving plane in the unit pixel. For example, one set of the pixel transistors is shared by two or four photoelectric conversion portions (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2004-172950, 2006-157953, and 2006-54276).
Additionally, there have been proposed techniques in which a microlens for focusing incident light on a light-receiving plane is disposed to each unit pixel, so that high sensitivity is implemented (for example, refer to Japanese Patent No. 2600250).
In addition, there have been proposed technologies in which a focusing efficiency is improved by measures such as optimization of the shape of an in-layer lens, reduction of the number of wire-line layers, or introduction of an optical waveguide, so that high sensitivity is implemented (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2002-314058 and 2003-324189).